Methods and apparatus for liquefaction of natural gas

ABSTRACT

A liquefaction unit that may include a first treating unit, a second treating unit, a liquefaction heat exchanger, a changeover unit, a liquid nitrogen tank, an LNG product storage tank, and a pressure build unit. During a first operating phase, the associated piping defines a first operating phase flow path for natural gas from the natural gas inlet stream to the first treating unit to the liquefaction unit to the LNG product stream, and a first operating phase flow path for nitrogen from the liquid nitrogen stream to the liquefaction unit to the second treating unit. During a second operating phase, the associated piping defines a second operating phase flow path for natural gas from the natural gas inlet stream to the second treating unit to the liquefaction unit to the LNG product stream, and a first operating phase flow path for nitrogen from the liquid nitrogen stream to the liquefaction unit to the first treating unit. During a changeover operating phase, the associated piping defines a changeover flow path for the natural gas from the natural gas inlet stream to the changeover treating unit to the liquefaction unit to the LNG product stream.

RELATED APPLICATION DATA

This patent application claims priority of U.S. Provisional Patent Application No. 62/201,377, filed Aug. 5, 2015, which is herein incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to apparatus and methods for liquefying natural gas. In another aspect, the present invention relates to apparatus and methods for liquefying natural gas that allows for switching process flow from a saturated treating unit to a purged treating unit without significant loss of natural gas, and in some embodiments without any loss of natural gas.

2. Description of the Related Art

There are numerous patents and publications relating to liquefaction of natural gas to form LNG of which the following are merely a few.

U.S. Patent Application Publication No. 20030154739 by Fanning et al., published Aug. 21, 2003, discloses natural gas liquefaction systems are provided wherein dependent trains including only cryogenic heat exchanger systems are serviced by common components in the system such that individual components need not be included in each dependent train for servicing that function. Further, the common components are positioned near the LNG storage tanks which, in turn, are typically located a substantial distance from the trains. This significantly reduces capital costs and allows boil-off gas from LNG storage tanks to be used for cooling in addition to being used as a fuel gas.

U.S. Patent Application Publication No. 20050217314 by Baudat, published October 6, 2005, discloses an apparatus for and process for recovering LNG from reservoir natural gas which includes circulating a portion of the natural gas thru a gas cooling loop that includes heat exchanges, an expansion zone and compression zone. The process also includes removing liquids from the gas cooling loop, distilling those liquids to recover a distilled gas. The process also includes compressing and expanding various portions of the distilled gas and passing those portions thru heat exchangers shared with the gas cooling loop to effect heating/cooling as desired. The process also includes removing a portion of the LNG cooling loop as LNG product.

U.S. Pat. No. 7,325,415 to Amin et al., issued Feb. 5, 2008, discloses novel processes and devices for the removal of freezable species such as carbon dioxide, water and heavy hydrocarbons from a natural gas feed stream during liquefaction to produce LNG are disclosed. The freezable species are able to be removed as a solid, avoiding the costly step of pretreatment to remove the freezable species from the natural gas feed stream prior to the liquefaction stage. The freezable species may be removed on a continuous basis being separated as solids following liquefaction of the natural gas feed stream with subsequent separation of the solids. The solid freezable species may then be liquefied on a continuous basis if required with natural gas recycled to the process. Continuous removal of the freezable species from the natural gas feed stream is achievable by maintaining cooling and separation apparatus at the same working pressure. Advantageously, at least part of the cooling vessel is constructed from a material having a low thermal conductivity which discourages formation of the solids of the freezable species on the walls of the cooling vessel.

U.S. Patent Application Publication No. 20110265494 by Barclay, published Nov. 3, 2011 discloses a liquefied natural gas production and storage scheme for offshore liquefaction of stranded gas reserves using a processing vessel and a liquefaction and storage shuttle vessel. The processing vessel includes the typical steps of condensate management, pre-treatment and compression. The processing vessel also recompresses a recycle gas from the LNG production and storage vessel. The high pressure, treated natural gas is fed to the LNG production and storage vessel that has minimal processing equipment consisting of at least a heat exchanger, an isentropic expander, a separator vessel, and a small LP compressor. The liquefier on the liquefaction and storage vessel are designed to generate a high liquid yield without the need for excessive operating pressures or multiple refrigerants circulating between vessels.

U.S. Patent Application Publication No. 20140130542 by Brown et al, published May 15, 2014, discloses a novel method and system for liquefying and distilling natural gas into high purity liquid methane (LNG) and NGL product streams. Heat exchangers and distillation towers are configured to produce high purity liquefied natural gas (LNG) and NGL product streams, while also rejecting excess nitrogen contained in the inlet gas stream, utilizing liquid nitrogen as the process refrigerant. A molecular sieve pretreatment system is configured to utilize the vaporized nitrogen stream for regeneration of the molecular sieve beds which are designed for removing water and carbon dioxide from the inlet gas stream.

U.S. Patent Application Publication No. 20140208797 by Kelley et al., published on Jul. 31, 2014, discloses a gas processing facility for the liquefaction of a natural gas feed stream is provided. The facility comprises a gas separation unit having at least one fractionation vessel. The gas separation unit employs adsorbent beds for adsorptive kinetic separation. The adsorbent beds release a methane-rich gas feed stream. The facility also includes a high-pressure expander cycle refrigeration system. The refrigeration system compresses the methane-rich gas feed stream to a pressure greater than about 1,000 psia. The refrigeration system also chills the methane-rich gas feed stream in one or more coolers, and then expands the chilled gas feed stream to form a liquefied product stream. Processes for liquefying a natural gas feed stream using AKS and a high-pressure expander cycle refrigeration system are also provided herein. Such processes allow for the formation of LNG using a facility having less weight than conventional facilities.

U.S. Patent Application Publication No. 20150276307, published by Ohart et al. on Oct. 1, 2015, discloses a method for producing liquefied natural gas (LNG) and separating natural gas liquids (NGLs) from the LNG. The method may include compressing natural gas to compressed natural gas, removing a non-hydrocarbon from the compressed natural gas, and cooling the compressed natural gas to a cooled, compressed natural gas. The method may also include expanding a first portion and a second portion of the cooled, compressed natural gas in a first expansion element and a second expansion element to generate a first refrigeration stream and a second refrigeration stream, respectively. The method may further include separating a third portion of the cooled, compressed natural gas into a methane lean natural gas fraction containing the NGLs and a methane rich natural gas fraction. The methane rich natural gas fraction may be cooled in a liquefaction assembly with the first and second refrigeration streams to thereby produce the LNG.

U.S. Patent Application Publication 20160047597, published by Brett et al. on Feb. 18, 2016, discloses methods and apparatus for the efficient cooling within air liquefaction processes with integrated use of cold recovery from an adjacent LNG gasification process are disclosed.

In spite of the many advances in the prior art, there are still needs in the art for methods and apparatus for liquefying natural gas.

These and other needs in the art will become apparent to those of skill in the art upon review of this specification, including its drawings and claims.

BRIEF SUMMARY OF THE INVENTION

It is an object of the present invention to provide for methods and apparatus for liquefying natural gas.

According to one embodiment of the present invention there is provided a natural gas liquefaction apparatus that may include associated piping and valves that interconnect one or more of the following: a natural gas inlet stream; a liquid nitrogen stream; a first treating unit; a second treating unit; a changeover treating unit; a liquefaction unit; and, an LNG product stream. During a first operating phase, the associated piping defines a first operating phase flow path for natural gas from the natural gas inlet stream to the first treating unit to the liquefaction unit to the LNG product stream, and a first operating phase flow path for nitrogen from the liquid nitrogen stream to the liquefaction unit to the second treating unit. During a second operating phase, the associated piping defines a second operating phase flow path for natural gas from the natural gas inlet stream to the second treating unit to the liquefaction unit to the LNG product stream, and a first operating phase flow path for nitrogen from the liquid nitrogen stream to the liquefaction unit to the first treating unit. And, during a changeover operating phase, the associated piping defines a changeover flow path for the natural gas from the natural gas inlet stream to the changeover treating unit to the liquefaction unit to the LNG product stream.

According to another embodiment of the present invention, these is provided, a method of liquefying natural gas. The method may include the steps of:

During a first operating stage, flowing the natural gas to a first treating unit to form treated natural gas, flowing the treated natural gas to the liquefaction unit to form LNG, and flowing liquid nitrogen to the liquefaction unit and then to a second treating unit;

During a second operating stage, flowing the natural gas to the second treating unit to form treated natural gas, flowing the treated natural gas to the liquefaction unit to form LNG, and flowing liquid nitrogen to the liquefaction unit and then to the first treating unit; and/or,

During a changeover operating stage, flowing the natural gas the a changeover treating unit to form treated natural gas, flowing the treated natural gas to the liquefaction unit to form LNG.

These and other embodiments are readily apparent to those of skill in the art upon review of this disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

The following drawing illustrates some of the many possible embodiments of this disclosure in order to provide a basic understanding of this disclosure. The drawing does not provide an extensive overview of all embodiments of this disclosure. The drawing is not intended to identify key or critical elements of the disclosure or to delineate or otherwise limit the scope of the claims. The following draw merely present some concepts of the disclosure in a general form. Thus, for a detailed understanding of this disclosure, reference should be made to the following detailed description, taken in conjunction with the accompanying drawing, in which like elements have been given like numerals.

FIG. 1 is a schematic flow diagram showing natural gas liquefaction system 10 of the present invention for condensing natural gas 100 into liquefied natural gas (“LNG”), which in the non-limiting embodiment shown may include treating unit 500, treating unit 600, liquefaction heat exchanger 700, change over unit 800, liquid nitrogen tank 200, LNG product storage 300, and pressure build unit 210.

DETAILED DESCRIPTION OF THE INVENTION

The methods, apparatus and products of the present invention may be utilized to liquefy natural gas to form liquefied natural gas (“LNG”).

The present invention relates to apparatus and methods for turning natural gas into liquefied natural gas (“LNG”). LNG is natural gas (predominantly methane with some mixture of ethane) that has been converted to liquid form for ease of storage or transport. Generally, LNG takes up about 1/600th the volume of natural gas in the gaseous state.

Referring now to FIG. 1, there is shown natural gas liquefaction system 10 of the present invention for condensing natural gas 100 into liquefied natural gas (“LNG”), which in the non-limiting embodiment shown may include treating unit 500, treating unit 600, liquefaction heat exchanger 700, change over unit 800, liquid nitrogen tank 200, LNG product storage 300, and pressure build unit 210.

Natural gas 100 is provided to system 10 through value 34. It should be understood that natural gas 100 fed into LNG plant 10 must be treated to remove at least water, carbon dioxide, and/or any other components that will freeze (e.g., benzene) under the low temperatures needed for storage or be destructive to the liquefaction facility. LNG typically contains more than 90 percent methane. It also contains small amounts of ethane, propane, butane, some heavier alkanes, and nitrogen. The purification process can be designed to give almost 100 percent methane.

Treating unit 500, treating unit 600 and change over unit 800 serve to treat the natural gas and remove the carbon dioxide, water and other components in the natural gas as required. Usually, the water content of the natural gas needs to be reduced to very low values (less than 1 ppmv) to prevent it from freezing and causing blockages during operation.

In FIG. 1 as shown, treating unit 500 and treating unit 600 are partitioned bed molecular sieve units with treating capacity that may be on the order of 8 hours, with changeover unit 800 having a treating capacity on the order of 15 minutes. Certainly, the treating capacity of these units may vary depending upon operating conditions, design parameters and/or economics, but in general, treating unit 500 and treating unit 600 will have rather treating capacity whereas the changeover unit 800 will have a treating capacity a very small fraction of those units. Generally, changeover unit will have a capacity that is sufficient to allow time for changeover between treating units 500 and 600 plus optionally some built in contingency time.

The liquefaction unit 10 operates alternatively between treating unit 500 and treating unit 600. During the short changeover between treating unit 500 and treating unit 600, process flow is routed through changeover unit 800 prior to being switched to the other treating unit.

To assist in regulating the process flow, system 10 also includes pairs of larger diameter valves (generally 3 inches) paired with smaller diameter valves (generally ¾ inch), specifically, 3 inch valves 21, 22, 24 and 25, paired respectively with ¾ inch valves 66, 67, 68 and 69. Certainly, any suitable sizes of valves may be utilized depending upon the process parameters and economics. And certainly, a single flow lone having a variable flow valve may be utilized instead of this parallel stream process.

Normal Operation Through Treating Unit 500

Normal operation though treating unit 500 is as follows. Natural gas 100 enters system 10 through valve 34 and will be routed to treating unit 500. Override selector 37 is in communication with flow controller 33, pressure controller 35, pressure controller 36, valve 36 and valve 38.

The natural gas flow path will be from the inlet through treating unit 500 on to the liquefaction unit 700 where it is converted into LNG and then onto LNG product storage tank 300, with all valves set to accomplish this. The nitrogen flow path will be from liquid nitrogen tank 200 through liquefaction unit 700 and onto and through treating unit 600 and/or changeover unit 800 and ultimately though the vent, with all valves set to accomplish this.

At startup after a changeover, treating unit 500 will be full of nitrogen, so natural gas 100 is initially provided to treating unit 500 through the smaller valve 66 to push out any remaining nitrogen through valve 62 and vent valve 65 to vent. Care is taken not to vent out any natural gas even if that means that some nitrogen may remain in the system with the natural gas. Once up and going, natural gas 100 is provided to treating unit 500 through the larger valve 21.

Upon exiting treating unit 500, the treated natural gas flows through valve 23 and into liquefaction unit 700 when the natural gas is liquefied into LNG.

Upon exiting liquefaction unit 700, the LNG passes through valve 33 and into LNG product storage tank 300. Pump 310 may be utilized to assist in transporting LNG product to its next destination, whether that be a pipeline or a tank or another operating unit.

At the same time that natural gas is making its way through system 10, liquid nitrogen flows from liquid nitrogen tank 200 through valve 12 and toward liquefaction unit 700. The liquid nitrogen is pressured to about 75 to 115 psig with pressure build unit PBU 210 by operating pressure control valve 11V in communication with controller 11C. The pressurized liquid nitrogen passes through control valve 31V and into liquefaction unit 700 where latent and sensible heat is exchanged between the natural gas and the nitrogen to cool and condense the natural gas and vaporize the nitrogen. Valve 31V controls the flow of liquid nitrogen into liquefaction unit 700, with valve 31V being controlled by temperature controller 31C on the LNG line exiting liquefaction unit 700. Nitrogen exiting liquefaction unit 700 then passes though optional heat exchanger 160 then onto treating unit 600 and/or changeover unit 800.

When making a changeover, treating unit 600 will be full of natural gas, so nitrogen is provided through smaller valve 69 to purge the natural gas to liquefaction unit 700 where it is liquefied and then routed to LNG product storage tank 300. After the natural gas is purged from treating unit 600, regeneration of treating unit 600 to remove water, carbon and other components is accomplished by heating the nitrogen exiting liquefaction unit 700 with heat exchanger 160 and providing that heated nitrogen to treating unit 600 through large valve 25 where it will heat molecular sieves and remove water, nitrogen and other components that were adsorbed from the natural gas in the last cycle. This nitrogen will then exit unit 600 and ultimately pass through valve 61 and vent valve 65 to vent.

Nitrogen is also provided to changeover unit 800. First it is provided through valve 43 to purge any natural gas from unit 800 out through valve 42 on its way to LNG product storage tank 300. Second nitrogen heated by heat exchanger 160 is provided through valve 43 to regenerate treating unit 600 to remove water, carbon and other components adsorbed from the natural gas.

The process will continue in this fashion until treating unit 500 approaches being saturated with carbon dioxide, at which time it is advisable to switch operations over to treating unit 600. This is accomplished to shutting down treating unit 500, utilizing changeover unit 800 during the change over, and starting up and switching over to treating unit 600.

Changeover Process

In the changeover, the incoming natural gas 100 ceases to be provided to treating unit 500 and is then routed though valve 41 to changeover unit 800 where the natural gas is treated to remove at least water, carbon dioxide, and/or any other components that will freeze (e.g., benzene) under the low temperatures needed for storage or be destructive to the liquefaction facility. Initially, natural gas is utilized to purge nitrogen in treating unit 800 out through valve 44 and value vent 65 to vent. Care is taken not to vent out any natural gas even if that means that some nitrogen may remain in the system with the natural gas. Once the nitrogen is purged out, natural gas exiting changeover unit 800 travels through valve 42 to liquefaction unit 700 where it is cooled into LNG. This LNG then travels through valve 38 to LNG storage tank 300. The flow of natural gas through changeover unit 800 will continue until treating unit 600 is up and running and treating natural. This flow through unit 800 during the changeover from unit 500 to unit 600 serves to maintain a minimum flow through the system to keep all equipment at the operating temperatures and pressures and reduce energy consumption.

In the changeover, natural gas is also routed to treating unit 600. Initially, treating unit 600 will be full of nitrogen, so natural gas 100 is initially provided to treating unit 600 through the smaller valve 67 to push out any remaining nitrogen through valve 61 and vent valve 65 to vent. Care is taken not to vent out any natural gas even if that means that some nitrogen may remain in the system with the natural gas. Once up and going, natural gas 100 is provided to treating unit 600 through the larger valve 22.

In the changeover, nitrogen is routed to treating unit 500. Initially, treating unit 500 will be full of natural gas, so nitrogen is provided through smaller valve 68 to purge the natural gas to liquefaction unit 700 where it is liquefied and then routed to LNG product storage tank 300. After the natural gas is purged from treating unit 500, regeneration of treating unit 500 to remove water, carbon and other components is accomplished by heating the nitrogen exiting liquefaction unit 700 with heat exchanger 160 and providing that heated nitrogen to treating unit 500 through large valve 24 where it will heat molecular sieves and remove water, nitrogen and other components that were adsorbed from the natural gas in the last cycle. This nitrogen will then exit unit 500 and ultimately pass through valve 62 and vent valve 65 to vent.

Normal Operation Through Treating Unit 600

Normal operation though treating unit 600 is essentially the same as through treating unit 500, except that the roles of units 500 and 600 have been reversed, and is as follows. Natural gas 100 enters system 10 through valve 34 and will be routed to treating unit 600. Override selector 37 is in communication with flow controller 33, pressure controller 35, pressure controller 36, valve 36 and valve 38.

The natural gas flow path will be from the inlet through treating unit 600 on to the liquefaction unit 700 where it is converted into LNG and then onto LNG product storage tank 300, with all valves set to accomplish this. The nitrogen flow path will be from liquid nitrogen tank 200 through liquefaction unit 700 and onto and through treating unit 500 and/or changeover unit 800 and ultimately though the vent, with all valves set to accomplish this.

At startup after a changeover, treating unit 600 will be full of nitrogen, so natural gas 100 is initially provided to treating unit 600 through the smaller valve 67 to push out any remaining nitrogen through valve 61 and vent valve 65 to vent. Care is taken not to vent out any natural gas even if that means that some nitrogen may remain in the system with the natural gas. Once up and going, natural gas 100 is provided to treating unit 600 through the larger valve 22.

Upon exiting treating unit 600, the treated natural gas flows through valve 26 and into liquefaction unit 700 when the natural gas is liquefied into LNG.

Upon exiting liquefaction unit 700, the LNG passes through valve 33 and into LNG product storage tank 300. Pump 310 may be utilized to assist in transporting LNG product to its next destination, whether that be a pipeline or a tank or another operating unit.

At the same time that natural gas is making its way through system 10, liquid nitrogen flows from liquid nitrogen tank 200 through valve 12 and toward liquefaction unit 700. The liquid nitrogen is pressured to about 75 to 115 psig with pressure build unit PBU 210 by operating pressure control valve 11V in communication with controller 11C. The pressurized liquid nitrogen passes through control valve 31V and into liquefaction unit 700 where latent and sensible heat is exchanged between the natural gas and the nitrogen to cool and condense the natural gas and vaporize the nitrogen. Valve 31V controls the flow of liquid nitrogen into liquefaction unit 700, with valve 31V being controlled by temperature controller 31C on the LNG line exiting liquefaction unit 700. Nitrogen exiting liquefaction unit 700 then passes though optional heat exchanger 160 then onto treating unit 500 and/or changeover unit 800.

When making a changeover, treating unit 500 will be full of natural gas, so nitrogen is provided through smaller valve 68 to purge the natural gas to liquefaction unit 700 where it is liquefied and then routed to LNG product storage tank 300. After the natural gas is purged from treating unit 500, regeneration of treating unit 500 to remove water, carbon and other components is accomplished by heating the nitrogen exiting liquefaction unit 700 with heat exchanger 160 and providing that heated nitrogen to treating unit 500 through large valve 24 where it will heat molecular sieves and remove water, nitrogen and other components that were adsorbed from the natural gas in the last cycle. This nitrogen will then exit unit 500 and ultimately pass through valve 61 and vent valve 65 to vent.

Nitrogen is also provided to changeover unit 800. First it is provided through valve 43 to purge any natural gas from unit 800 out through valve 42 on its way to LNG product storage tank 300. Second nitrogen heated by heat exchanger 160 is provided through valve 43 to regenerate treating unit 500 to remove water, carbon and other components adsorbed from the natural gas.

The process will continue in this fashion until treating unit 600 approaches being saturated with carbon dioxide, at which time it is advisable to switch operations back over to treating unit 500. This is accomplished to shutting down treating unit 600, utilizing changeover unit 800 during the change over, and starting up and switching over to treating unit 500.

The liquefaction process is continued in this fashion of alternating natural gas treatment back and forth between treating unit 500 and treating unit 600, with use of the changeover unit 800 all as described above.

All patents and patent publications cited in this application are herein incorporated by reference.

The present disclosure is to be taken as illustrative rather than as limiting the scope or nature of the claims below. Numerous modifications and variations will become apparent to those skilled in the art after studying the disclosure, including use of equivalent functional and/or structural substitutes for elements described herein, use of equivalent functional couplings for couplings described herein, and/or use of equivalent functional actions for actions described herein. Any insubstantial variations are to be considered within the scope of the claims below. 

1. A natural gas liquefaction apparatus comprising: associated piping and valves that interconnect the following: a natural gas inlet stream; a liquid nitrogen stream; a first treating unit; a second treating unit; a changeover treating unit; a liquefaction unit; and, a LNG product stream; wherein during a first operating phase, the associated piping defines a first operating phase flow path for natural gas from the natural gas inlet stream to the first treating unit to the liquefaction unit to the LNG product stream, and a first operating phase flow path for nitrogen from the liquid nitrogen stream to the liquefaction unit to the second treating unit; wherein during a second operating phase, the associated piping defines a second operating phase flow path for natural gas from the natural gas inlet stream to the second treating unit to the liquefaction unit to the LNG product stream, and a first operating phase flow path for nitrogen from the liquid nitrogen stream to the liquefaction unit to the first treating unit; and, wherein during a changeover operating phase, the associated piping defines a changeover flow path for the natural gas from the natural gas inlet stream to the changeover treating unit to the liquefaction unit to the LNG product stream.
 2. A method of liquefying natural gas comprising the steps of: During a first operating stage, flowing the natural gas to a first treating unit to form treated natural gas, flowing the treated natural gas to the liquefaction unit to form LNG, and flowing liquid nitrogen to the liquefaction unit and then to a second treating unit; During a second operating stage, flowing the natural gas to the second treating unit to form treated natural gas, flowing the treated natural gas to the liquefaction unit to form LNG, and flowing liquid nitrogen to the liquefaction unit and then to the first treating unit; and, During a changeover operating stage, flowing the natural gas a changeover treating unit to form treated natural gas, flowing the treated natural gas to the liquefaction unit to form LNG. 